1. Technical Field of the Invention
This invention relates to a butterfly valve for shutting off or regulating the flow of a fluid along a flow path.
2. Description of the Prior Art
A butterfly valve is a well known form of valve comprising a disc-shaped valve member, which is rotatably mounted in a valve orifice for movement about a diametral axis. Butterfly valves are commonly used as throttle valves in petrol and gas engines, and as flow control valves in fluid pipelines.
UK Patent No. GB203119B discloses a butterfly valve for connecting in series with a fluid pipeline, the valve comprising an annular body portion defining a valve orifice and a disc-shaped valve member rotatably mounted in the orifice and having a frusto-conical side wall. The valve member is mounted to a diametral shaft which extends perpendicular to the through-axis of the annular valve body. An externally-mounted actuator is provided for rotating the disc-shaped valve member between an open position (in which it extends parallel to the through-axis of the valve body) and a closed position (in which it extends perpendicular to the through-axis of the valve body across the valve orifice).
When closed, a seal on the frusto-conical side wall of the disc-shaped valve member seals against a complimentary surface of an annular valve seat fitted concentrically to the valve body around the orifice therein.
In use, the valve member seal and valve seat wear against each other as the valve is opened and closed, to the extent that the valve begins to leak when closed. In order to overcome this problem, both the valve seat and valve member seal are replaceable items which are secured in situ by bolts.
A disadvantage of the above-mentioned arrangement is that fluid can leak through the gaskets which are interposed between the valve seat and the valve body, and between the valve member and the valve member seal.
We have now devised a butterfly valve which is less susceptible to leakage and which comprises component parts which can be replaced without compromising the integrity of the valve.